Improve organizational clarity by separating tests from utility modules
used in tests, and also pave the way for re-using these utilities for UI
outside the sidebar app in future (eg. src/annotator/).

Improved tag editor (Part 2/2)

- Fix add new tag bug in Edge
- Remove tag-editor’s Chrome hack fix to limit suggestions to 20
- Add ARIA 1.1 Combobox  a11y model to TagEditor

Add accessibility unit test using axe-core

"default" is the default name for an a11y scenario unless one is
specified.

Remove the global react/display-name lint suppression for the
src/sidebar/components/test directory with individual line-level
suppressions.

The reason for having a global rule wasn't obvious when looking at
.eslintrc and there aren't that many occurrences.

Improve handling of text in RTL languages

This enables axe-core tests which depend on CSS rules being available to
work, such as checking that elements have sufficient color contrast.

Remove obsolete references to shallow rendering

`checkAccessibility` calls often violate this rule because the `content`
key is assigned a function which returns an element, but is not actually
a component.

Add Datalist component (Part 1/2)

- Use as a replacement for the native <datalist> tag
- Fix UI differences between Chrome, FF, Safari and Edge with respect to the <datalist>
- Fix performance issues experienced in Chrome when used with <datalist>
- Allow for future enhanced customization of list including substring highlighting that <datalist> could not do

Add infrastructure for running a11y tests using axe-core and add an
initial set of tests for existing components. A small number of
components (3) fail these checks. These tests have been temporarily
skipped so that we can incrementally fix them later.

One trivial issue with an un-labeled link in `LoggedOutMessage` was fixed by
adding a `title` attribute.

We replaced use of Enzyme's shallow rendering for component unit tests
some time ago in https://github.com/hypothesis/client/pull/1470.

Add eslint-plugin-jsx-a11y to the lint configuration

Bump cross-env from 6.0.3 to 7.0.0

Bump fetch-mock from 8.3.1 to 8.3.2

Bump sinon from 8.1.0 to 8.1.1

This helps detect accessibility errors in markup as part of `make lint`.

Flag the current set of known errors with a `FIXME-A11Y` comment and
suppress them temporarily, so that we can fix them incrementally while guarding
against new errors.

Part of #1727

Bump codecov from 3.6.1 to 3.6.2

Bump mocha from 7.0.0 to 7.0.1

Bump autoprefixer from 9.7.3 to 9.7.4

Bumps [autoprefixer](https://github.com/postcss/autoprefixer) from 9.7.3 to 9.7.4.
- [Release notes](https://github.com/postcss/autoprefixer/releases)
- [Changelog](https://github.com/postcss/autoprefixer/blob/master/CHANGELOG.md)
- [Commits](https://github.com/postcss/autoprefixer/compare/9.7.3...9.7.4)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [aws-sdk](https://github.com/aws/aws-sdk-js) from 2.606.0 to 2.610.0.
- [Release notes](https://github.com/aws/aws-sdk-js/releases)
- [Changelog](https://github.com/aws/aws-sdk-js/blob/master/CHANGELOG.md)
- [Commits](https://github.com/aws/aws-sdk-js/compare/v2.606.0...v2.610.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [@octokit/rest](https://github.com/octokit/rest.js) from 16.36.0 to 16.38.3.
- [Release notes](https://github.com/octokit/rest.js/releases)
- [Commits](https://github.com/octokit/rest.js/compare/v16.36.0...v16.38.3)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [mocha](https://github.com/mochajs/mocha) from 7.0.0 to 7.0.1.
- [Release notes](https://github.com/mochajs/mocha/releases)
- [Changelog](https://github.com/mochajs/mocha/blob/master/CHANGELOG.md)
- [Commits](https://github.com/mochajs/mocha/compare/v7.0.0...v7.0.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [cross-env](https://github.com/kentcdodds/cross-env) from 6.0.3 to 7.0.0.
- [Release notes](https://github.com/kentcdodds/cross-env/releases)
- [Changelog](https://github.com/kentcdodds/cross-env/blob/master/CHANGELOG.md)
- [Commits](https://github.com/kentcdodds/cross-env/compare/v6.0.3...v7.0.0)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [codecov](https://github.com/codecov/codecov-node) from 3.6.1 to 3.6.2.
- [Release notes](https://github.com/codecov/codecov-node/releases)
- [Commits](https://github.com/codecov/codecov-node/compare/v3.6.1...v3.6.2)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [sinon](https://github.com/sinonjs/sinon) from 8.1.0 to 8.1.1.
- [Release notes](https://github.com/sinonjs/sinon/releases)
- [Changelog](https://github.com/sinonjs/sinon/blob/master/CHANGELOG.md)
- [Commits](https://github.com/sinonjs/sinon/compare/v8.1.0...v8.1.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [fetch-mock](https://github.com/wheresrhys/fetch-mock) from 8.3.1 to 8.3.2.
- [Release notes](https://github.com/wheresrhys/fetch-mock/releases)
- [Commits](https://github.com/wheresrhys/fetch-mock/compare/v8.3.1...v8.3.2)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Improve display of user-controlled text in Right-To-Left (RTL) languages
by applying the `dir="auto"` attribute to:

 - Input fields (annotation body editor, search bar)
 - The rendered annotation body's container element
 - The rendered annotation quote (ie. the `<blockquote>` element)

This will cause these elements to switch to their "base" direction for
text layout [1] to RTL or LTR automatically depending on the content
[2].

Fixes https://github.com/hypothesis/lms/issues/1372

[1] https://www.w3.org/International/articles/inline-bidi-markup/uba-basics
[2] https://www.w3.org/International/questions/qa-html-dir

Fix Menu tab focus on keyboard navigation

The Publish Annotation popup menu button was not showing a focus halo on keyboard navigation.  This was due to the child content of the button.menu__toggle having position:absolute elements and so that was not providing a width or height directly on the focusable button.

Removing the absolute styling and instead using a flex layout remedies this, but there also needs to be a block display applied to the button.toggle_menu element so can be treated as a flex item, rather than flex container, with a height of 100% to match the size of its parent “.menu”.  In order to ensure everything still laid out the same, namely the {label} and {menuIndicator}, a pseudo flex container “.menu__toggle-wrapper” needed to be added.

Additionally, the triangle content is moved from DOM to css so it is not read out by screen readers.

Move more annotation-related state logic into sub-components, store

Add a temporary bit of logic to instantiate drafts of new (non-highlight)
annotations. Also add a wrapper div to `AnnotationPublishControl` for
better layout.

Update `AnnotationThread` to render EITHER `Annotation` or `AnnotationOmega`
based on feature-flag setting, not both at the same time. This avoids
potential state contention between the two components.